UV inkjet printers have been widely used in professional commercial output applications (e.g. advertisements, posters, high-quality art reproductions etc.) because they allow printing on various types and thicknesses of materials at relatively high printing speeds and has stable and uniform printing quality. With its reliable performance, the time and labor invested in preparing color separation plates is eliminated, which enables faster printing.
In commercially available UV inkjet printers at present, an inkjet module controlled to travel back and forth is provided on a sliding platform of the machine. A plurality of inkjet cartridges are provided on the inkjet module and a plurality of print heads corresponding to the respective inkjet cartridges are provided at the bottom of the inkjet module. Inks are ejected from nozzles located at the bottom of the print heads onto a substrate to be printed. The inks jetted on the substrate to be printed are then quickly hardened (cured) by subjecting them to UV light from a UV lamp provided at a side of the inkjet module. During printing of the substrate, a region of interest traditionally can be printed using a unidirectional printing method or a bi-directional printing method to save print time.
In order for a printed product to display a rich color scale, a color separating software can be used for color separation of the UV inkjet printer, which separates the printing of an image to be printed into multiple passes based on the file size and resolution of the image, such that the print heads print the data to be printed in multiple passes. Refer to the printing methods and devices proposed in U.S. Pat. Nos. 5,469,198 and 5,923,349 for more details on the multi-pass printing techniques.
If a transparent glossy surface finish is desired on the substrate to be printed, a layer of varnish is typically applied after inks are printed on the patterns at every region of interest on the substrate, and then the varnish is temporarily set (semi-cured) by a UV lamp at a low energy, or the varnish is first left untouched. Once printing of the entire substrate is finished, the whole inkjet module then returns to the starting point and completely cures the varnish jetted on the regions by the UV lamp with 100% energy. As a result, a transparent glossy layer is formed on the patterns by such a delayed curing process. The finished product will have a transparent textured surface.